CVE-2020-12820Network attack vector

Authenticated daemon crash via oversized filename

Published Dec 19, 2024 · Updated Dec 20, 2024

Stack-based buffer overflow in Fortinet FortiOS 5.6.0 through 5.6.12 and 6.0.0 through 6.0.10 allows remote authenticated users to crash fcnacd. fcnacd fails to reject an oversized FortiClient filename before it overwrites a stack buffer. Exploitation requires an SSL VPN session with FortiHeartbeat and Endpoint-Compliance enabled on the same interface; arbitrary code execution remains undemonstrated.

CVSS severity8.8
High
EPSS probability0.86%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stack-based buffer overflow in Fortinet FortiOS 5.6.0 through 5.6.12 and 6.0.0 through 6.0.10 allows remote authenticated users to crash fcnacd. fcnacd fails to reject an oversized FortiClient filename before it overwrites a stack buffer. Exploitation requires an SSL VPN session with FortiHeartbeat and Endpoint-Compliance enabled on the same interface; arbitrary code execution remains undemonstrated.

The record

CVE
CVE-2020-12820
Published
Dec 19, 2024
Updated
Dec 20, 2024
Vendor
Fortinet
Product
FortiOS
Classifications
CWE-121, CWE-787, T1499.004
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Dec 19, 2024CVE publishedPublication date reported by the CVE source.
  2. Dec 20, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=5.6.0 <=5.6.12
  2. Affected versionversion=6.0.0 <=6.0.10

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Fortinet · FortiOSversion=5.6.0 <=5.6.12; version=6.0.0 <=6.0.10

Published CVSS scores

8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
5.4FortinetCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-121Stack-based Buffer Overflow
CWE-787Out-of-bounds Write
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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